IONOSAR

Knowledge about forest above-ground biomass and how it is are changing is of fundamental importance in quantifying how the Earth's carbon cycle and climate behave, and is also crucial in assessing forest resources and the services they provide to mankind. For most parts of the world, in particular the tropical forests, information on biomass is currently very limited, at very coarse scales, and subject to large and unquantified errors. Getting a better handle on the biomass in these forests is therefore an essential part of knowing how forests contribute to climate change and supporting UN negotiations on measures to protect them. In response to this urgent need, an international team led by UK and French scientists proposed the BIOMASS satellite mission to the European Space Agency for the third cycle of Earth Explorer Core missions. In competitive assessments, this was first selected to be one of six missions out of 29 proposed for further study, and in March 2009 was one of the remaining three selected for Phase A Study. If all goes well and BIOMASS passes a further assessment in 2011, it will launch in 2016-17. Over the five-year mission lifetime, it will map the full range of the world's above-ground biomass with accuracy and spatial resolution compatible with the needs of national scale inventory and carbon flux calculations, and will map changes in forest biomass. These data are crucial for improving our assessments of the current and future carbon cycle, and have important ramifications for the water cycle and human use of the biosphere. The mission also has several important secondary objectives, including gathering new information on polar ice, soil moisture, ocean salinity, and sub-surface structures and palaeo-hydrology in arid areas. BIOMASS takes advantage of a new opportunity, since before 2003 the long radar wavelength it uses (68 cm) was unavailable for Earth Observation because of possible interference with military systems. However, in 2003 the International Telecommunication Union opened this wavelength for imaging the Earth. This was a key development, since measurements of forests at this long wavelength are very sensitive to biomass. However, along with the special capabilities of long wavelength radar come special problems. In particular, the radar signals used by BIOMASS have to travel through the ionosphere, which can affect them in a variety of ways. Hence a key step in ensuring the selection and success of BIIOMASS is to develop strategies for dealing with these effects. Part of this strategy is to choose the orbit carefully, because the ionosphere varies enormously with position, time of the day and year, and conditions on the Sun. So we can choose an orbit that reduces the effects; to do this requires extensive knowledge about ionospheric behaviour, and part of the research will be devoted to building up this knowledge and relating it to radar performance. However, it is clear that there are conditions under which we will need ways to correct the data, and much of the research will be devoted to developing and testing methods to do this. Its end point will be a set of procedures that tell us how make accurate measurements of forest biomass and height under whatever ionospheric conditions BIOMASS encounters, and thus ensure the mission can deliver its ambitious science goals.